Embodiments of the present invention are directed to a neutralization system, and more particularly, to a neutralization system with interleaved periods of sampling and neutralization to optimize neutralization of a target object.
Air ionization is an effective method of eliminating static charges on target surfaces. Air ionizers generate large quantities of positive and negative ions in the surrounding atmosphere that serve as mobile carriers of charge in the air. As ions flow through the air, they are attracted to oppositely charged particles and surfaces. Neutralization of electrostatically charged surfaces can be rapidly achieved through this process.
Air ionization may be performed using electrical ionizers, which generate ions in a process known as corona discharge. Electrical ionizers generate air ions by intensifying an electric field around a sharp point until the field overcomes the dielectric strength of the surrounding air. Negative corona discharge occurs when electrons are flowing from the electrode into the surrounding air. Positive corona discharge occurs as a result of the flow of electrons from the air molecules into the electrode.
Ionizer devices, such as an alternating current (AC) or direct current (DC) charge neutralizing system, take many forms, such as ionizing bars, air ionization blowers, air ionization nozzles, and the like, and are utilized to neutralize static electrical charge by emitting positive and negative ions into the workspace or onto the surface of an area. Ionizing bars are typically used in continuous web operations such as paper printing, polymeric sheet material, or plastic bag fabrication. Air ionization blower and nozzles are typically used in workspaces for assembling electronics equipment such as hard disk drives, integrated circuits, and the like, that are sensitive to electrostatic discharge (ESD).
Neutralization output can be adjusted in response to the determination of charge on the target object. FIG. 1 is a schematic block diagram of an exemplary prior art neutralization system 10. A target, such as a moving web 12 having an undesirable charge thereon is passed by an ionizer bar 14 with ionizers, such as pins, generating positive and negative ions. Downstream of the ionizer bar 14 is an external sensor 16 that detects a residual charge on the moving web 12. Data from the sensor 16 is passed into a controller 20 disposed within a housing 18 and coupled to one or more high voltage power supplies 22a, 22b, which are in turn coupled to the ionizer bar 14. Based on the sensor data, the controller 20 generates and outputs signals representing adjustments necessary to the output of the high voltage power supplies 22a, 22b in order to optimize neutralization on the target web 12. The high voltage power supplies 22a, 22b are coupled to the ionizer bar 14 by one or more high voltage cables 24.
The use of a downstream sensor has significant drawbacks, such as the need for additional costly equipment and connecting cables that may be too large or awkward to practically place into the workspace. Some sensors may also not be approved for placement in hazardous locations (e.g., areas at risk of fire or explosion hazards).
In addition, over time, an ionizer may accumulate debris. In order to maintain optimal performance of the ionizer, it is necessary to clean the ionizer in order to remove the debris. As an ionizer accumulates debris, the ionizer's charge will decrease and, therefore, the current flowing from the voltage supply into the ionizer will also decrease. A method for having the ionization self-calibrate and indicate performance is described in U.S. Pat. No. 8,039,789, the entire contents of which are incorporated by reference herein. However, the method requires the initial accumulation of calibration data for a plurality of operating states of the high voltage power supply. Real-time data, in particular a sum of the current output to the positive and negative ionizers, acquired during operation is then compared to the closest data point to determine a difference in performance. The accumulation of calibration data for what may be 250 or more data points can be time consuming, and requires a large memory space to store the necessary baseline table.
It is desirable to provide a static neutralization system that can optimize neutralization of a target object without the need for an external downstream sensor.